In his first act as president, Biden asked the nation to join in a moment of silent prayer for those who have died due to the COVID-19 pandemic.

“We've been through so much in this nation,” Biden said during his inaugural address. “In my first act as president, I’d like to ask you to join me in a moment of silent prayer to remember all those who we lost in this past year to the pandemic, those 400,000 fellow Americans -- moms, dads, husbands, wives, sons, daughters, friends, neighbors and co-workers.”

“We'll honor them by becoming the people and the nation we know we can and should be,” he added.

On Tuesday, the death toll from COVID-19 surpassed 400,000 people in the U.S.

In a speech that stood in sharp contrast to his predecessors’ message of “American carnage,” Biden quoted Abraham Lincoln, before making his own commitment to devote his time in office to uniting the nation and calling on Americans to open their souls to each other, too.

"In another January, on New Year's Day in 1863, Abraham Lincoln signed the Emancipation Proclamation. When he put pen to paper, the president said, and I quote, “if my name ever goes down into history, it’ll be for this act, and my whole soul is in it," Biden said.

“My whole soul is in it," Biden continued to applause. "Today, on this January day, my whole soul is in this: bringing America together, uniting our people, uniting our nation. And I ask every American to join me in this cause."

He also took a moment to recognize the historic nature of Kamala Harris being sworn-in as the nation’s first woman and South Asian woman, to become vice president.

“Here we stand, looking out on the great mall where Dr. King spoke of his dream. Here we stand where, 108 years ago at another inaugural, thousands of protesters tried to block brave women marching for the right to vote. And today, we mark the swearing of the first woman in American history elected to national office, Vice President Kamala Harris.”

-ABC News' Molly Nagle and Justin Gomez

Biden is delivering his first speech since taking the oath of office and assuming the office of the presidency moments before on the West Front of the U.S. Capitol -- calling on Americans to meet in this moment with a united front and start fresh without political divisions.

"This is democracy's day, a day of history and hope, of renewal and resolve. Through a crucible for the ages, America has been tested anew. And America has risen to the challenge," Biden began. "Today we celebrate the triumph, not of a candidate, but of a cause -- the cause of democracy."

"We've learned again that democracy is precious," Biden said from the steps stormed, two weeks before, by a pro-Trump mob. "Democracy is fragile. And at this hour, my friends, democracy has prevailed."

Speaking directly to the nation, Biden called country's current state a "historic moment of crisis and challenge" but said "unity is the path forward" and asked Americans to "start fresh" and "begin to listen to one another again."

"Politics doesn't have to be a raging fire, destroying everything in its path. Every disagreement doesn't have to be a cause for total war. And we must reject the culture in which facts themselves are manipulated, and even manufactured," he said.

President Joe Biden has taken the oath of office -- becoming the 46th president of the United States.

Supreme Court Chief Justice John Roberts administered the oath of office.

Roberts congratulated Biden as "Mr. President."

"Hail to the Chief" then played for the first time for Biden.

The oath comes after nearly 50 years in public life for Biden, three tries for the White House and after a victory delayed by vote counts, complicated by potential legal challenges and unacknowledged by the outgoing president.

Laying his hand on the massive Biden family bible held by his wife, Jill Biden, Biden ended the oath with a signature grin on his face.